In general, in order to manufacture a desired semiconductor integrated circuit, various processes including a film-forming process, an etching process, an oxidation-diffusion process, an annealing process or the like are carried out repeatedly to a substrate such as a semiconductor wafer. When the various processes are carried out, a necessary gas corresponding to a kind of the process, for example a film-forming gas for a film-forming process, ozone gas for an annealing process or an etching gas for an etching process (including a plasma etching process), is introduced into a processing container.
In the above case, the atmosphere in the processing container has been evacuated in order to maintain a pressure suitable for the kind of the process. It is requested that the evacuated gas flows uniformly with respect to the surface of the semiconductor wafer, in order to highly maintain uniformity of the process within the surface.
Herein, a conventional general processing unit for removing a natural oxidation film (SiO2) or the like deposited on the surface of a semiconductor wafer by using plasma (for example, Japanese-Translated Patent Laid-Open Publication of PCT application No. 2000-511700) is explained. FIG. 7 is a schematic structural view of a conventional general processing unit of single-fed type. FIG. 8 is a plan view of a portion including the stage in FIG. 7.
As shown in FIG. 7, the processing unit using plasma has a processing container 2, for example having a cylindrical shape and made of aluminum. In the processing container 2, a stage 6 is arranged on a tip end of a hollow and wide supporting arm 4 that extends from a side wall of the container. A semiconductor wafer W is adapted to be placed on the stage 6. A large numbers of gas holes 7 that introduce a process gas, such as a plasma gas including Ar gas, H2 gas and so on, into the processing container 2 are arranged at an upper portion of the sidewall of the processing container 2 in a circumferential direction thereof.
A ceiling part of the processing container 2 is open. A ceiling dome 8 having a cylindrical shape and a closed ceiling is hermetically arranged on the ceiling part. The ceiling dome 8 is made of for example quartz. An inductive coupling coil 10 is wound on an outside wall of the ceiling dome 8. A high-frequency wave of for example 450 kHz is adapted to be applied from a high-frequency electric power source 12 for inductively coupled plasma to the inductive coupling coil 10.
The stage 6 is made of for example ceramics such as aluminum nitride (AlN). A resistance heater 14 and a bias electrode 16 are buried (incorporated) in the stage 6. The resistance heater 14 is connected to an electric power source for heater. The bias electrode 16 is connected to a high-frequency electric power source 16 for biasing, which generates a high-frequency wave of for example 13.56 MHz.
A discharging pipe 18 with a large aperture is connected to a central portion of a bottom part of the processing container 2. The discharging pipe 18 extends downward and linearly by a predetermined length. A flow-way adjusting valve 20 and a vacuum pump 22 are provided in that order in the discharging pipe 18 in order to evacuate the processing container 2. The vacuum pump 22 consists of for example a turbo molecular pump. In addition, a flange at an outlet port of the vacuum pump 22 is connected to a discharging duct 24. Thus, the discharged gas is adapted to flow into a final gas abatement system (not shown).